Summer Triangle

The Summer Triangle is an astronomical asterism in the northern celestial hemisphere. Its defining vertices form a triangle and are Altair, Deneb, and Vega, each the brightest star of its constellation (Aquila, Cygnus, and Lyra, respectively). The greatest declination is +45° and the lowest is +9°, meaning the three stars can be seen from all parts of the Northern Hemisphere and from much of the Southern Hemisphere. The stars in Aquila and Cygnus represent the head of an eagle and tail of a swan, respectively, which appear inscribed within the triangle and form its altitude of the triangle. Two small constellations, Sagitta and Vulpecula, lie between Aquila in the south of the triangle and Cygnus and Lyra to the north.